9.1 About HugePages

The HugePages feature enables the Linux kernel to manage large
pages of memory in addition to the standard 4KB (on x86 and
x86_64) or 16KB (on IA64) page size. If you have a system with
more than 16GB of memory running Oracle databases with a total
System Global Area (SGA) larger than 8GB, you should enable the
HugePages feature to improve database performance.

Note

The Automatic Memory Management (AMM) and HugePages features are
not compatible in Oracle Database 11g and later. You must
disable AMM to be able to use HugePages.

The memory allocated to huge pages is pinned to primary storage,
and is never paged nor swapped to secondary storage. You reserve
memory for huge pages during system startup, and this memory
remains allocated until you change the configuration.

In a virtual memory system, the tables store the mappings between
virtual addresses and physical addresses. When the system needs to
access a virtual memory location, it uses the page tables to
translate the virtual address to a physical address. Using huge
pages means that the system needs to load fewer such mappings into
the Translation Lookaside Buffer (TLB), which is the cache of page
tables on a CPU that speeds up the translation of virtual
addresses to physical addresses. Enabling the HugePages feature
allows the kernel to use hugetlb entries in the
TLB that point to huge pages. The hugetbl
entries mean that the TLB entries can cover a larger address
space, requiring many fewer entries to map the SGA, and releasing
entries that can map other portions of the address space.

With HugePages enabled, the system uses fewer page tables,
reducing the overhead for maintaining and accessing them. Huges
pages remain pinned in memory and are not replaced, so the kernel
swap daemon has no work to do in managing them, and the kernel
does not need to perform page table lookups for them. The smaller
number of pages reduces the overhead involved in performing memory
operations, and also reduces the likelihood of a bottleneck when
accessing page tables.